Motorcycle Repair: 1986 pw50 wont stay running, yamaha pw50, box lid

Question
just bought this yamaha pw50 for my little ones to learn on, but i cant get this thing to run, replpaced the ignition coil, rebuild kit for carb, it will turn over start for a few seconds then die, i consider my self a pretty decent mechanic. but im still learning small engine repair, any advice will help, thanks

Answer
Jose, Im not sure what to tell you but try to eliminate some areas. The fuel valve at bottom of tank could have a restriction and not letting fuel into the carb. It could be the igniter or CDI box or it could be that the exhaust pipe could be plugged up with an oily build up and wont let the engine breath. Or as simple as the air box lid off and it wont slow the air down to draft the fuel through the carb. Check some of these areas to help narrow down the problem.